"There's just a few medications on the market that work, and even these can be inadequate," Sisley said. "They end up getting stuck on eight, 10, 12 different medications, and after taking so many, suddenly they're like zombies."

Some of these patients though were starting to feel better. They also seemed much more present. She wanted to know what was making a difference. They told her they found an alternative to all those medicines.

They were self-medicating with marijuana.

"I was really stunned and more and more patients were coming out of the shadows and disclosing to me that they were having some useful experiences with the marijuana plant," Sisley said.

She appreciated the progress they said they were making, but like any good scientist she didn't want to rely on anecdotal evidence. She wanted documented proof, clinical trials of large patient populations that run in the gold standard of a peer-reviewed journal that marijuana was the right approach to treating PTSD, or any other ailment for that matter. People use it to treat a variety of medical issues, such as multiple sclerosis, arthritis, epilepsy, glaucoma, HIV, chronic pain, Alzheimer's, cancer and others.

With medical marijuana legal in nearly half of the states, more doctors are wondering what impact this drug really has on people. They ask for dosage information. They want to know about its long-term impact on patients.

Sisley looked for answers to these questions in medical research, but she didn't see much. When she decided to do the studies herself and applied for federal approval, she was met with miles of red tape and resistance -- like many other researchers before her.

That's because marijuana is one of the tightest-controlled substances under federal law. The U.S. government considers it a Schedule I drug, meaning the Drug Enforcement Administration considers it to have no medical value. It's right up there with heroin and LSD. To do research on marijuana, scientists need approval from several federal departments. And that approval is rare.

Most marijuana studies focus on the harm caused by the plant. The studies on its medicinal qualities are small, early stage or observational at best. "Mainstream physicians won't come near the stuff, even if they hear that it works, because without the research, without it approved in legitimate practice guidelines, they are going to worry about their license and their professionalism," Sisley said. "That's why it is key to have randomized control trials for this to work."

A bipartisan bill -- from Rand Paul, R-Kentucky, Cory Booker, D-New Jersey, and Kirsten Gillibrand, D-New York --called the Compassionate Access, Research Expansion, and Respect States Act of 2015 was introduced in the Senate in March that would ease some of those restrictions and make it easier to study the drug. But the legislation is in committee at the moment. If it does ever pass, and scientists can begin studying the drug in earnest, there are several areas they may target in addition to PTSD.

Here are 10 of them, based on the ailments people commonly use medical marijuana to treat. Again, because there is such limited research on this topic, these areas are based on results that CNN would typically not report on because the work is in a far too early stage to see if it really works. But that is the point some doctors and medical researchers are making.

AIDS/HIV

In a human study of 10 HIV-positive marijuana smokers, scientists found people who smoked marijuana ate better, slept better and experienced a better mood. Another small study of 50 people found patients that smoked cannabis saw less neuropathic pain.

Alzheimer's

Medical marijuana and some of the plant's chemicals have been used to help Alzheimer'spatients gain weight, and research found that it lessens some of the agitated behavior that patients can exhibit. In one cell study, researchers found it slowed the progress of protein deposits in the brain. Scientists think these proteins may be part of what causes Alzheimer's, although no one knows what causes the disease.

Studies are contradictory, but some early work suggests it reduced exercise-induced asthma. Other cell studies showed smoking marijuana could dilate human airways, but some patients experienced a tight feeling in their chests and throats. A study in mice found similar results.

Cancer

Animal studies have shown some marijuana extracts may kill certain cancer cells. Other cell studies show it may stop cancer growth, and with mice, THC, the psychoactive ingredient in marijuana, improved the impact of radiation on cancer cells. Marijuana can also prevent the nausea that often accompanies chemotherapy treatment used to treat cancer.

Chronic pain

Some animal and small human studies show that cannabinoids can have a "substantial analgesic effect." People widely used them for pain relief in the 1800s. Some medicines based on cannabis such as Sativexare being tested on multiple sclerosis patients and used to treat cancer pain. The drug has been approved in Canada and in some European countries. In another trial involving 56 human patients, scientists saw a 30% reduction in pain in those who smoked marijuana.

Crohn's disease

In a small pilot study of 13 patients watched over three months, researchers found inhaled cannabis did improve life for people suffering from ulcerative colitis and Crohn's disease. It helped ease people's pain, limited the frequency of diarrhea and helped with weight gain.

Epilepsy

Medical marijuana extract in early trials at the NYU Langone Medical Center showed a 50% reduction in the frequency of certain seizures in children and adults in a study of 213 patients recently.

Glaucoma

Glaucoma is one of the leading causes of blindness. Scientists have looked at THC's impact on this disease on the optic nerve and found it can lower eye pressure, but it may also lower blood pressure, which could harm the optic nerve due to a reduced blood supply. THC can also help preserve the nerves, a small study found.